Lunar and Planetary Science XXXVII (2006)
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Mineral and Lithologic Mapping of Martian Low Albedo Regions Using OMEGA Data. M. Zhu 1, 2, H. Xie2,
H. Guan2, R.K. Smith2, 1Research Center of GIS and RS, East China Institute of Technology, Fuzhou, Jiangxi
344000, China, [email protected], 2Earth & Environmental Science, University of Texas at San Antonio, San
Antonio, TX, 78249, USA, [email protected]
Introduction: Since January 2004, OMEGA/Mars
Express data has revealed a diverse and complex
Martian surface mineralogy [1]. The important findings,
together with Thermal Emission Spectrometer (TES),
Thermal Emission Imaging System (THEMIS), and insitu observations from Mars Exploration Rovers,
include but not limited to (1) hydrated sulfates [1, 2, 3,
4, 5, 6, 7]; (2) iron oxides and oxhydroxides [2, 3, 5, 8,
9, 10, 11, 12, 13]; (3) hydrated alteration phyllosilicates
[4, 2, 3]; and (4) mafic and ultramafic rocks containing
pyroxene and olivine [1, 11, 13, 14, 15, 16]. These
results are improving our knowledge regarding the
Martian surface mineralogy and lithology, and the
geological history of Mars. OMEGA imagery as noted
above provides efficient and satisfactory hyperspectral
information. It can be used not only to map individual
minerals, but also their corresponding lithologic units.
The purpose of this study was to identify the
mineral and lithologic units using the OMEGA
imagery. The minimum noise fraction (MNF) method
was applied to derive the lithologic endmember units
and then three spectral matching methods, spectral
angle mapper (SAM), spectral feature fitting (SFF), and
binary encoding (BE), were used to match minerals and
lithologies. Three low albedo areas, Meridiani Planum,
Ophir-Candor Chasma, and Syrtis Major, were chosen
for this study. Meridiani Planum is Opportunity Rover’s
landing site. Minerals such as pyroxene, hematite,
jarosite, and phyllosilicates and lithologies such as
basalt have been identified [2, 3, 11, 12]. The hydrated
sulfates (kieserite and polyhydrated sulfates) on lighttoned layered terrains at the Ophir and Candor Chasmas
have been detected [1, 5]. Syrtis Major is dominated by
basalts, but with little olivine [13, 17]. These are
available for testing results of this study.
Dataset: OMEGA acquires spectrum in 352
contiguous bands covering 0.35 to 5.1 µm with a spatial
resolution of 0.3 to 4 km/pixel and spectral resolution
of 7 to 20 nm [1]. The spectral range and resolution
have been chosen to allow for identification of major
surface and atmospheric species by their diagnostic
spectral absorption feature [1]. OMEGA data for three
selected areas were downloaded from the ESA’s
Planetary Science Archive. In this study, we mainly
examined the spectral range from 0.4 to 2.5 µm. The
data was pre-processed using a modified IDL program
initially provided by ESA to a relative reflectance
image (I/F), which was then utilized for atmospheric
corrections using a LLEE model developed by Guan et
al. [18].
Method: The atmospherically corrected image was
then processed using ENVI for image classification and
mineral and lithologic identification. The MNF method,
conducted twice principal component analysis, was first
run to produce noise-free principal components. The
MNF band1 mostly contains the albedo information,
but the MNF bands 2, 3, and 4 mainly contain the
mineral and lithologic information, which can be used
to produce a false-color endmember map (Fig.1).
Spectra of these endmembers were then processed to
match with the various standard spectral libraries from
the USGS, John Hopkins University, and Brown
University. Three spectral matching methods (SAM,
SFF, and BE) were applied based on both spectra
and/or continuum removal spectra for scoring
individual minerals and lithologies from libraries with
each endmember. The highest scores for the matched
minerals and lithologies were then recorded for each
endmember.
Fig. 1 RGB images of MNF bands 2, 3, and 4. a.
ORB0529-3, red dot is Opportunity landing site; b.
ORB0548-3; c. ORB0444-3
Results: ORB0529-3 (Maridiani Planum) consists
of 8 lithologic endmemebers (Fig.1-a). (1) The green
endmember on Fig.1-a match best with basalt and
basaltic andesite. Comparable minerals include
chalcopyrite, hematite, and pyroxene. The diagnostic
spectral absorption bands in continuum-removed curves
are 0.47 µm, 0.96 µm, and 1.91µm. These compositions
are more comparable to the Noachian highland basaltic
rocks detected by TES [15, 17], named the Crater Unit
and Dissected Unit of the Plateau Sequence on USGS
geologic maps. (2) The purple endmember, which
includes the Opportunity landing site, matches best with
the minerals chalocpyrite, hematite and jarosite. The
shape of this purple colored area is counterpart to
hematite-bearing material mapped by TES [8] and
THEMIS [10]. It should be noted that chalcopyrite has
yet to be reported however. Lithologies showing the
Lunar and Planetary Science XXXVII (2006)
best matches include basalt, sandstone, and andesite.
This may infer that the rock type is basaltic sandstone
or sand. However, the spectral absorption bands 0.5
µm, 0.9 µm, 1.91 µm, and 2.2 µm, respectively in
continuum-removed curves match well with micasandstone (Fig.2-a). The existing sandstone or sand
most likely came from the erosion of the south
highlands basalts. The Opportunity Rover has proved
that the soil consists of fine-grained basaltic sand and a
surface lag of hematite-rich spherules; the finely
laminated rocks, silicate sediments, contain abundant
sulfate salts with embedded hematite-rich spherules [3].
(3) The pink endmember, north of the purple unit to the
mid-east portion of the area, matches very well with the
minerals barite, jarosite and hematite. The most
compatible lithologies for this area are basalt and micasandstone. This indicates that the basaltic rich
sediments are well developed in the layered and etched
terrains. (4) The yellow unit matches garnet
(almandine) and hematite, while the lithology matchs
basalt as well as felsic granite. This suggests the
presence of more feldspar in this endmember. (5) The
red, blue, and gray endmembers occur in the northwest
region of the studied image. Barite, hematite, and
gypsum match well with these endmembers and their
lithology of basaltic sandstone.
Ophir-Candor Chasmas (Fig.1-b) consists of 6
lithologic endmembers. The yellow endmember at the
Chasmas floor is best matched with basalt and norite.
Minerals matching the yellow unit are monticellite,
pyoxene, hematite, and covellite. The red endmember,
associated with the elevated hills in Chasma, is the
light-toned layered terrain and is best matched with
basalt and siltstone (possibly basaltic siltstone).
Minerals matching this unit are monticellite, anhydrite
and gypsum. Kieserite is also possible. Kieserite was
mapped by [5]. The green endmember located at the top
of the cliff edge and blue endmember located on the
northern end of Ophir Chasma is interpreted to be
basaltic andesite, with hematite and orthoclase (?).
Syris Major (Fig.1-c) consists of 7 lithologic
endmembers. The yellow endmember in the southwest
portion of the area suggests basalt. The matched
minerals include pyroxene and hematite. The purple
endmember, most notably in the southeast portion of
the area, is best matched with diabase and basalt.
Minerals matching the purple endmember include
garnet (uvarovite), monticellite, and pyroxene. The red
endmember of the near center of some craters matches
with basalt or minerals thenardite, pyroxene, and garnet
(uvarovite). If thenardite (Na2SO4) is truly present, this
is the first time it has been reported to occur on the
Martian surface. The diagnostic spectral absorption
bands 1.17 µm, 1.42 µm, 1.91- 2.01 µm, 2.11 µm, and
2.47 µm, respectively match well with thenardite
(Fig.2-b). Thenardite is one of several non-marine
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evaporate sulfate minerals formed in playa basins. If
this mineral does exist on the Martian surface, it
suggests that water existed in the area. The coral
endmember in the northwest of the area is basaltic
andesite, with garnet (uvarovite) and hematite.
Fig.2 Continuum removal spectra of ORB0529-3 purple
endmember with its matched lithologies (a) and of
ORB0444-3 red with minerals (b)
Summary: Comparisons with previous studies
suggests that (1) The lithology of the Crater Unit and
Dissected Unit in the southern Meridiani Planum
(ORB0529_3) consists of basalt and basaltic andesite.
The mineralogy includes pyroxene, chalcopyrite and
hematite. The remainder of the study area including the
Opportunity landing site is mainly basaltic sandstone or
basaltic sand, though the etched terrain, as well as the
portion to the north and west, found more barite and
gypsum in addition to hematite. (2) Two different
lithologic groups are identified in Ophir-Candor
chasma. The lithology on the Chasma floor, with low
albedo, is basalt or norite, and the matched minerals are
monticellite, pyoxene, hematite, and covellite. The
second lithology (i.e. Slide Materials and Highly
Deformed Terrain Material) is basaltic andesite, with
the presence of orthoclase and hematite. Regions of the
light-toned layered terrain are dominated by
monticellite, anhydrite, and gypsum. (3) Rocks in low
albedo areas of Syrtis Major are basalts and possible
diabase. The mineralogy includes pyroxene,
monticellite, Garnet (uvarovite), hematite, and
thenardite. This is the first time that the thenardite is
reported to occur on the surface in Martian surface
based on its diagnostic spectral absorption bands at 1.17
µm, 1.42 µm, 1.91- 2.01 µm, 2.11 µm, and 2.47 µm.
Acknowledgements: The authors would like to
thank Yves Langevin, John Mustard, Joe Zender, and
Aline Gendrin for their directions on the OMEGA data
pre-processing and atmospheric corrections.
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